Process for reducing nitroanilines



Patented Dec. 11, 1951 UNITED STATES PATENT OFFICE c PROCESSv FOR REDUCING NITRQANLINE Sy HaroldlVon Bramer, J ames E: Magofl'n, and Milton Clemens, Kingsport, Tenn., assignors to` Eastman Kodak Company, Rochesten N. Y., a.; corporation ofiNewJersey Application April 1,6, 1948, Serial No. 21,428

This invention relates to a process for preparingaromatic primary amines by the reduction of the corresponding aromatic nitro compounds.

Itis known that aromatic nitro compounds can be either catalytically or chemically reduced to aromatic primary amines. The methods heretofore used for this purpose require-long periods of time and yieldproducts which usually are contaminated by-impurities. In attempting'to produce purer products it has been customary to purify the starting materials as thoroughly as possible before reduction.` Even so, when strong acids, such as sulfuric acid, have been used, the resulting amine is discolored due to side-reactions. For example, when p-nitroaniline is made by the ammonolysisv ofV p-chloronitrobenzene, before the p-nitroaniline is reduced to p-phenylenediamine, a purication of the p-nitroaniline is usually made to increase the yieldl and Ipurity of product. One ofthe methods previously used comprises reducing the aromatic nitrocompound with iron and dilute hydrochloric acid. p-Phenylenediamine, for example, is usually made by the reduction of p-nitroaniline, which has been puri fied, by the action of' iron filings and hydrochloric acid at temperatures ofy 80 to 100 C. The reaction is generally carried out in large tubs, equipped with heavy-duty agitators. Thus, only a portion of ithe p-nitroaniline can becharged at one time, the remainder being added from time to time as the reaction proceeds. Similarly, the iron filings cannot be added at one time, the remainder being gradually'added over a period of time. Operating in this manner the reaction. is slow and may reqllire fromlO to l2hours for completion. Moreover,y the p-nitroaniline used in this process must be-ffree fromcontamination, and the p-phenylenediamine produced mustk be recrystallized or vacnum` distilled. Because lof thisineiiicient method of production, p-phenylenediamine is an expensivevchemicaLandfull use ofits chemical potentialtiesA asl a rawy material; for synthesis is inhibited.

We have now foundL that aromatic primaryamines canI be prepared cheaply and in much less time than has been previously possible. We have further found that whenr the aromatic primary amines are to be produced bythe reduction of aromatic nitro compounds in accordancewith the processof. ourinvcntion, itis` unnecessary to first purify thefarcmatic: nitro compelled prior. t reduction..

Itis, accordingly, anobjectofv our invention to. l,

provide a process for theY production of aromatic primary, amines. A` further object is to provide` aprocessl for reducing a nitro aromatic primary amineto an aromatic primary diamine. further object. is to provide a process for reducing aromatic .nitro compounds in about half the time,

- or less, than has been previously necessary. An-

other object of our invention is to provide a process, for reducing aromatic nitro compounds to thecorresponding aromatic primary amines without first purifying the aromatic nitro compounds. Other objects will become apparent from 4a consideration of the following description.

According to the process of our invention, we prepare aromatic primary amines byreducing aromatic nitro compounds without first purifying the aromatic nitrocompounds. Advantageously, our reduction can be carried out by passing superheated steam over the aromatic nitro compound', and introducing the resulting vapors of steam and the aromatic nitro compound into a reduction system. We have found that when an aromatic nitro compoundr is-.reduced in this manner, the reduction takes place at the moment the aromatic nitro compound condenses'in'the reduction system, and the time consumed is only about half that ordinarily required. The reaction mixture resulting' from the reduction can then be usedy directly in the preparation of other compounds, asin the production of Nsubstituted compounds,v

or can be separated into its component parts by:

and p-nitrotoluenes, 0, m, and p-nitroanilines, 3, 4 5.-, and G-nitrQ-o-toluidines, 2, 4,-, 5, and G-nitrQ-m-toluidines, 2-, and 3-nitro-p-toluidines; a-and; enitronaphthalenes, l-nitro-l-naphthyl'- amine, lr-nitro-Z-naphthylamine, etc.

Thefolowing description will serve to illustratethel manner whereby we prepare one of the pri.

mary amines, p-phenylenediamine, which canA conveniently beprepared according to the process;

of our invention.

The accompanying drawing illustrates, sche- @tical-1y@ apparatus. suitable forv @arrangeur invention none of its embodiments.` The drawing shows-A a still l0 equipped with a feed line Il suppliedwlih a shutfoff valve. The still is COR- nested. with an ejector I2 which is connected to.

A Still` a conduit I3 which leads to a reservoir I4. A line I5 extends from the bottom of the reservoir to a pump IB which drives liquids through a line II back to the ejector I2 and thence to the reservoir I4, so that a circulating stream of liquids can be maintained. Extending from the line I'I between the pump I6 and the ejector is a take-off line I8 equipped with a shut-off valve which leads to a filter I9. From the top of the reservoir I4 a conduit 20 leads to a cyclone-type separator 2| which feeds back any small amounts of p-nitroaniline and p-phenylenediamine (or other aromatic nitro compound) vaporized or entrained with the water from the reservoir, through a conduit 22. The top of the cyclone separator is connected by a line 23 to a steam-jet ejector 24 which serves to draw a vacuum on the reservoir.

In accordance with one embodiment of our invention, 13.13 pounds of crude p-ntroaniline, which Was conveniently prepared by the ami monolysis of p-chloronitrobenzene and contained water and other impurities, were fed into the still Ill through the inlet line II. Cold water was then added to the conduit I3 by a line (not shown), and then circulated through the reservoir I4 to the pump I6 through the discharge line I 5, and from the pump to the ejector I2 through the discharge line I1 of the pump. The circulation of the cold water through the ejector I2 was sufiicient to create a vacuum of about 15 inches of mercury in the still I0, and this was adjusted to about 2 to 5 inches of mercury by the addition of air to the still through the inlet line II. The still was then slowly heated, and the removal of water from the crude p-nitroaniline was cuite rapid. After the temperature reached 150 C., removal of water was substantially complete. The water circulating through the ejector I2 was then heated to about 85 C., and 1.465 pounds of iron dust and 0.0182 pound of sulfuric acid, per pound of p-nitroaniline in the still I0, were added to the water circulating through the ejector I2. The air vent (not shown) to the still was closed, and steam superheated to a temperature of about 200 C. was passed over the dried, molten p-nitroaniline and thence to the ejector I2. While the temperature of the stillpot I0 remained at 190 to 200 C., distillation occurred, and a mixture of water and p-nitroaniline vapors, in a ratio of approximately to 1 passed from the still through the ejector I2 and into the conduit I 3. Both the water and p-nitroaniline vapors were condensed by the rapidly moving stream in the conduit I3, and the p-nitroaniline was immediately reduced by the iron dust to p-phenylenediamine. The concentration of Water in the circulating steam in the conduit I3 was' kept substantially constant by passing steam through the ejector 24 thus creating a vacuum in the reservoir I4, which caused rapid removal of water through the line 20 connected to the cyclone separator 2|. Any small amounts of p-nitroaniline and p-phenylene-diamine vaporized or entrained were condensed in the separator 2| and returned to the reservoir I4 by the line 22 connected to the bottom of the separator, While the water vapors escaped from the top of the separator through a line connected to the ejector 24.

After all of the p-nitroaniline had been distlled from the still I0, the volume of liquid in the conduit I3, reservoir I4, and the connecting lines I5 and I'I, was adjusted by the addition of water (or evaporation by means of the steam-jet ejector 24 when too much water was in the system) until a free-flowing mass was obtained which could be easily handled. The sulfate ions dissolved in the liquor were removed by careful neutralization with barium hydroxide, and while the reaction slurry was still hot it was passed from the circulating stream in the line I'I through the discharge line I8 into the lter I9 where all of the iron oxide and barium sulfate were removed. The ltrate consisted of a clear, hot solution of p-phenylenediamine which could conveniently be used directly in the preparation of other compounds, if desired.

In order to obtain pure p-phenylenediamine, the liquor containing the p-phenylenediamine was cooled slowly with constant agitation, so that uniform crystals of p-phenylenediamine were produced. When crystals no longer formed, the slurry was centrifuged in an inert atmosphere, e. g., nitrogen, and then conveyed from the centrifuge to a vacuum drying apparatus, Where all water was removed. There were thus obtained 9.8 pounds, representing a yield of 96%, of p-phenylenediamine in the form of a powder, which darkened only slightly when exposed to the air.

The mother liquor from the centrifuging operation can be returned to the reduction system as a part of the charge for the next reduction, or it can be conveyed to an evaporator Where it can be concentrated. The concentrated solution can then be allowed to crystallize, and a second crop of p-phenylenediamine crystals obtained. This mother liquor is also suitable for any use where an aqueous solution of p-phenylenediamine is acceptable.

While the above example described the preparation of p-phenylenediamine, it is to be understood that other aromatic primary amines can be prepared equally well. Likewise, the conditions used in our process can be varied widely, and depend largely on the properties of the nitro compound being reduced. For example, the reduced nitro compound need not be separated from the reduction system in the manner described above, but can be separated by any of the methods known to those skilled in the art (e. g. extraction, crystallization, distillation, decantation, etc.). For some purposes it is not necessary to treat the reduction liquor further since the untreated liquor is useful for the further synthesis of other organic compounds, e. g. the N-substitutled amines, dyes, etc.

The amount of metallic iron and sulfuric acid used in the reduction of the nitro compund can also be varied. By suitable adjustment of the concentration of the sulfuric acid and using an iron dust of proper activity, it is possible to reduce the nitro compound substantially as fast as it is condensed in the reduction system. When p-nitroaniline was reduced, it was found that best results were obtained when 1.465 pounds of iron and 0.0182 pound of sulfuric acid were used for each pound of p-nitroaniline reduced. The pH of the reduction liquor is a wandering ngure without significance, varying from strongly acid to weakly basic as the reduction proceeds. The pH can be maintained at any desired figure by the addition of more acid as the reaction progresses.

- The temperatures used in the various steps of our process can be varied considerably and are generally a function of the nitro compound bei ing reduced. For the reduction system We have found that a temperature of about C. gives the best results, however, temperatures from' (5G-90 C. can be used, if desired. Similarly, when steam superheated to a temperature of about 200 C. is used, the temperature in the still 5 remains at about 190 to 200 C. and the distillation of the nitro compound into the reduction system is more eiiicient. This temperature of the steam can be varied widely, however, depending upon the temperature at which the various nitro compounds become volatile with steam. Temperaatures of from 150 to 350 C. can be used, a1- though temperatures of from 175 to 225 C. are generally sufficient.

Mineral acids other than sulfuric acid have been found to be useful in the practicing the process of our invention. Typical acids include sulfuric acid, hydrochloric acid, phosphoric acid, etc. Likewise, metals other than iron can be used. We have found that aluminum is especially useful where iron is not easily available.

While the process of our invention is particularly useful in the reduction of crude or unpurified aromatic nitro compounds, it is likewise useful for reducing pure compounds, since not only are the yields higher, and the time required for reduction much less, but the aromatic primary amines produced are much purer and darken only slightly when exposed to air. The products of the prior art processes, on the other hand, are darker, probably due to the large contact time necessary to complete reduction, and usually must be recrystallized or otherwise puried before use.

It is to be understood that the drawing appended hereto is merely a schematic diagram of our invention, and that various modifications thereof can be made by those skilled in the art without departing from the spirit and scope of our invention.

What we claim and desire to secure by Letters Patent of the United States is:

1. In a process for reducing a nitroaniline to a phenylenediamine, the steps which comprise passing steam heated from 150 C. to 350 C. over the nitroaniline, and introducing the resulting vapors of steam and the nitroaniline into a reducing system, consisting of an aqueous mineral acid selected from the group consisting of sulfuric acid, phosphoric acid and hydrochloric acid and metallic iron, and maintained at a temperature of from 60 C. to 90 C. where the said vapors are condensed and the nitroaniline contained in the steam distillate is reduced to a phenylenediamine.

2. In a process for reducing a nitroaniline to a phenylenediamine, the steps which comprise passing steam heated from 150 C. to 350 C. over the nitroaniline, and introducing the resulting vapors of steam and the nitroaniline into a reducing system, consisting of aqueous sulfuric acid and metallic iron, and maintained at a temperature of from 60 C. to 90 C. Where the said vapors are condensed and the nitroaniline contained in the steam distillate is reduced to a phenylenediamine.

3. In a process for reducing a nitroaniline to a phenylenediamine, the steps which comprise passing steam heated from 150 C. to 350 C. over the nitroaniline, and introducing the resulting vapors e5 of steam and the nitroaniline into a reducing system, consisting of aqueous phosphoric acid and metallic iron, and maintained at a temperature of from C. to 90 C. where the said vapors are condensed and the nitroaniline contained in the steam distillate is reduced to a phenylenediamine.

4. In a process for reducing a nitroaniline to a phenylenediamine, the steps which comprise passing steam heated from C. to 350 C. over the nitroaniline, and introducing the resulting vapors of steam and the nitroaniline into a reducing system, consisting of aqueous hydrochloric acid and metallic iron, and maintained at a temperature of from 60 C. to 90 C. where the said vapors are condensed and the nitroaniline contained in the steam distillate is reduced to a phenylenediamine.

5. In a process for reducing p-nitroaniline to p-phenylenediamine, the steps which comprise passing steam heated from C. to 225 C. over p-nitroaniline, introducing the resulting vapors of steam and p-nitroaniline into a circulating stream, consisting of aqueous sulfuric acid and metallic iron, and maintained at a temperature of from 60 C. to 90 C. where the said vapors are condensed and the p-nitroaniline in the steam distillate is reduced to p-phenylenediamine.

6. In a process for reducing p-nitroaniline to p-phenylenediamine, the steps which comprise passing steam heated from 175 C. to 225 C. over p-nitroaniline, introducing the resulting vapors of steam and p-nitroaniline into a circulating stream, consisting of aqueous phosphoric acid and metallic iron, and maintained at a temperature of from 60 C. to 90 C. where the said vapors are condensed and the p-nitroaniline in the steam distillate is reduced to p-phenylenediamine.

7. In a process for reducing p-nitroaniline to p-phenylenediamine, the steps which comprise passing steam heated from 175 C. to 225 C. over p-nitroaniline, introducing the resulting vapors of steam and p-nitroaniline into a circulating stream, consisting of aqueous hydrochloric acid and metallic iron, and maintained at a temperature of from 60 C. to 90 C. where the said vapors are condensed and the p-nitroaniline in the steam distillate is reduced to p-phenylenediamine.

HAROLD VON BRAMER. JAMES E. MAGOFFIN. MILTON CLEMENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,292,879 Kise Aug. 11, 1942 2,402,440 Owen June 18, 1946 2,415,402 Audrieth et al Feb. 11, 1947 2,415,817 Gohr etal Feb. 18, 1947 2,431,585 Rout Nov. 25, 1947 2,432,087 Brown Dec. 9, 1947 2,446,519 Bean Aug. 10, 1948 FOREIGN PATENTS Number Country Date 279,283 Great Britain Oct. 21, 1927 

1. IN A PROCESS FOR REDUCING A NITROANILINE TO A PHENYLENEDIAMINE, THE STEPS WHICH COMPRISES PASSING STREAM HEATED FROM 150* C. TO 350* C. OVER THE NITROANILINE, AND INTRODUCING THE RESULTING VAPORS OF STEAM AND THE NITROANILINE INTO A REDUCING SYSTEM, CONSISTING OF AN AQUEOUS MINERAL ACID SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID, PHOSPHORIC ACID AND HYDROCHLORIC ACID AND METALLIC IRON, AND MAINTAINED AT A TEMPERATURE OF FROM 60* C. TO 90* C. WHERE THE SAID VAPORS ARE CONDENSE AND THE NITROANILINE CONTAINED IN THE STREAM DISTILLATE IS REDUCED TO A PHENYLENEDIAMINE. 